I took a chunk of nylon thread and my leather needle and ran a string from the trigger guard through the top of the valve stem. When I am ready to shoot, as I cock the hammer I flick the stem off with a finger, and it just hangs from the bottom of the rifle out of the way until I need it again.

So far it has worked great and acts as a secondary safety. Also it is easy to get and if I loose it I have a bag with about 60 more caps in it.... I am not going to mess with wax when I have that.